Communalisms: Epiphytic association

• Epiphytic association occurs when one organism grows on the surface of another organism without harming the later one.
• Example; the epiphytic bacteria grows on the skin surface of many plant species.
• They also colonize on the surface of algae. Bacterial population also grows on the skin surface generally exhibiting commensal relationship with human beings.

Synergism/proto co-operation

• Synergism between two population indicates that both of the population benefit from the relationship but the association is not obligatory i.e. independent.
• Both populations can survive independently, although they get benefit from the synergistic relationship.

Mutualism/Symbiosis

• It is an obligatory interrelationship between two populations and from this association both of the partners are benefited.
• It is the extension of synergism allowing population to unite and establish as single unit population that can occupy habitats in unfavorable condition for their extension.
• It leads to the evolution of new organisms like:

1. Lichens : between algae and fungi
2. Rhizobium: in the root nodules of legumes
3. Azolla-BGA association
4. Mycorrhizal relationship (soil fungi)

Parasitism

• An association between parasites and hosts is called as parasitism.
• The parasites are an organism which lives on or in the body of another organisms i.e. hosts.
• Parasites get the benefit of both shelter and food from their host, e.g.: some species of fungi, viruses and bacteria.